1. Field of the Invention
The present invention relates to an electron gun for a color TV, or a high definition industrial picture tube, and more particularly, to a focusing electrode in an electron gun for a color cathode ray tube which can reduce man-power and number of components in a fabrication of the electron gun and can prevent a center electron beam from being elongated horizontally depending on a fitted depth of an inner guide electrode.
2. Discussion of the Related Art
The electron gun in a color cathode ray tube is a device for forming a pixel by focusing three electron beams emitted from cathodes onto a fluorescent screen of red, green and blue fluorescent materials inside of a cathode ray tube screen.
FIG. 1A illustrates a cross section of an exemplary background art in-line type electron gun, disclosed in Japanese Laid Open Patent Application(A) No. S61-250933 dated Nov. 8, 1986, and FIG. 1B illustrates a perspective view of the first, and second focusing electrodes shown in FIG. 1A.
Referring to FIGS. 1A and 1B, an electron gun 1 is comprised of a triode 2 for forming electron beams and a main focusing lens 3 for focusing the electron beams. The triode 2 is provided with cathodes 4 for emitting thermal electron beams, a control electrodes 5 for controlling the thermal electrons, and an accelerating electrode 6 for accelerating the thermal electrons. The main focusing lens 3 disposed next to the triode 2 comprises a focusing electrode 7 having a first focusing electrode 71 to which a low static voltage is applied a second focusing electrode 72 of to which a high dynamic voltage is applied synchronous to a deflection of the electron beams, and an anode 8 disposed next to the second focusing electrode 72 to which a positive voltage is applied. The first focusing electrode 71 has a face 713 fitted with flat electrodes 712 vertical to the face 713 on both sides of each of three electron beam pass-through holes 711, and the second focusing electrode 72 has a face 723 opposite to the first focusing electrode 71 fitted with one pair of flat electrodes 722 on an upper and a lower parts of three electron beam pass-through holes 721 toward the cathodes. Upon application of the voltages to the respective electrodes, the electron beams are controlled and accelerated by powers from the control electrode 5 and the accelerating electrode 6. Then, the electron beams pass through a dynamic quadrupole lens formed by a voltage difference between the low static voltage of the first focusing electrode 71 and the high voltage of the second focusing electrode 72. The dynamic quadrupole lens converges the electron beams in a horizontal direction because the first focusing electrode 71, a low voltage and involved in converging of electron beams, has the vertical flat electrodes 712 fitted in a horizontal direction of the face 713 thereof, and, thereafter, the beam diverges the electron beams in a vertical direction because the second focusing electrode 72, involved in diverging of electron beams, has the horizontal flat electrodes 722 fitted on upper part and lower part of the electron beam pass-through holes 721 in the face 723 thereof. Accordingly, the dynamic quadrupole lens elongates the electron beams in a vertical direction. The vertically elongated electron beams are then converged by the main focusing static lens formed by a voltage difference between the second focusing electrode 72 and the anode 8. Finally, the electron beams are accelerated toward the screen by the positive voltage and deflected by a non-uniform magnetic field formed by deflection yokes(not shown). Though the non-uniform magnetic field can correct mis-convergence, the non-uniform magnetic field elongates the electron beams in a horizontal direction, causing a haze coming from a thin image dispersion on upper and lower parts of an electron beam spot on the screen. However, as the electron beams are elongated in a vertical direction by the dynamic quadrupole lens, the electron beams are not elongated in the horizontal direction by the non-uniform magnetic field, but forms a good electron beam spot.
However, this background art electron gun has a problem in that the separately forming and welding of the horizontal flat electrodes 712 and the vertical flat electrodes 722 on the first, and second focusing electrodes 71 and 72 at faces thereof increases production time. Also, the horizontal flat electrodes 712 and the vertical flat electrodes 722 are susceptible to distortion by an external impact during transportation, storage and fabrication. Further, the electrodes 712 and 722 do not easily weld vertically on respective faces 713 and 723 of the first, and second focusing electrodes 71 and 72, thereby causing a problem that a quality of the electron gun cannot be maintained uniform.
FIG. 2A illustrates a cross section of an exemplary background art in-line type electron gun with another type of focusing electrode disclosed in Japanese Laid Open Patent Application (A) No. H2-72546 dated Mar. 12, 1990, and FIG. 2B illustrates a section across line I--I shown in FIG. 2A. Herein, parts that are identical to the previous background art of FIG. 1 are given the same numerals.
The focusing electrode 7 comprise a first focusing electrode 71 to which a low static voltage is applied and a second focusing electrode 72 to which a high dynamic voltage is applied synchronous to a deflection of the electron beams. The first focusing electrode 71 has a face 713 with a single horizontally elongated electron beam pass-through hole 711 formed therein and an inner guide electrode 73 with three electron beam pass-through holes 731 formed therein disposed at an inner side of the face 713, and the second focusing electrode 72 has a face 723 opposite to the first focusing electrode 71 and fitted with one pair of horizontal flat electrodes 722 toward the cathodes on upper and lower parts of three electron beam passthrough holes 721. Upon application of the dynamic voltage to the second focusing electrode 72, a dynamic quadrupole lens is formed between the face 713 of the first focusing electrode 71 with the single electron beam pass-through hole 711, the horizontal flat electrodes 722 and the inner guide electrode 73. The dynamic quadrupole lens diverges the electron beams in a vertical direction because the second focusing electrode 72, which diverges the electron beams, has the horizontal flat electrodes on upper and lower parts of the electron beam pass-through holes 721. In addition to this, by adjusting a fitted depth of the inner guide electrode 73 in the first focusing electrode 71, power of the dynamic quadrupole lens may be adjusted, which provides a versatile electron gun that can be used in color cathode ray tubes of multiple models. This eliminates cumbersome designs of the first and second focusing electrodes required for different power of the dynamic quadrupole lens for color cathode ray tubes of similar models.
However, this electron gun has a problem in that, when the inner guide electrode 73 is fitted deeper toward the cathodes 4 in the first focusing electrode 71, a center electron beam is involved in decreases of horizontal focusing power and vertical diverging power, resulting in horizontally elongating the center electron beam.